1. Technical Field
The present disclosure relates to a method and an apparatus for inspecting a wafer surface. More particularly, the present disclosure relates to a method for automatically adjusting a position in a dark field inspection apparatus to inspect a wafer surface and an apparatus for performing same.
2. Discussion of the Related Art
As design scales become minute, trivial defects that were not critical previously become critical, thereby resulting in lower productivity. Therefore, an inspection apparatus having extended precision is required. Additionally, a method of precisely controlling the apparatus is required.
In a process of manufacturing a semiconductor device, an inspection process may be classified into three sub processes.
A first sub process is an efficiency inspection of an inspection apparatus. A criterion wafer is loaded in the inspection apparatus. Then, an inspected value is obtained and compared with a criterion value of the criterion wafer to examine the efficiency of the inspection apparatus.
A second sub process is an inspection to detect a cause of abruptly lowered productivity.
A third sub process is an inspection to detect defects of a wafer that has undergone some of the manufacturing process.
One of the known apparatuses for inspecting a wafer surface uses laser scattering. A laser is irradiated at a predetermined angle onto a surface of an objective wafer that is to be inspected. Then, a scattered laser caused by defects on the wafer surface is detected to examine defects. The laser is irradiated onto the objective wafer by the Raster scan method, and the laser has a specific spot size. Therefore, in order to scan the entire surface of the objective wafer, a plurality of the Raster scannings may be performed thereon.
In detecting the scattered laser, a detector having mirrors that condense the scattered laser and a photo multiplier tube (PMT) may be used. The PMT outputs an electric serial signal having a varying amplitude in accordance with the strength of the scattered laser. Then, a computer analyzes the outputted electric serial signal. When an electric serial signal that exceeds a limit is detected, the objective wafer is judged to have defects.
In examining whether or not the laser is irradiated on the wafer exactly, an auto position system (APS) may be used. The APS not only detects a position where the laser is reflected according to height difference of the wafer, but also detects the height difference.
FIG. 1 is a flow chart showing a conventional method of inspecting a wafer surface.
Referring to FIG. 1, in step S10, a wafer is loaded in an apparatus for inspecting a wafer surface, and a laser is irradiated onto an inspection region of a wafer. Then, in step S20, a portion of the laser may be scattered on an inspection region of the wafer, and a detector detects the scattered laser to inspect a surface of the inspection region of the wafer. In step S30, a remaining portion of a laser that is reflected on the wafer surface of the inspection region is detected in order to analyze a height of the wafer. Then, in step S40, the height of the wafer is compensated for by position analysis. Then, in step S50, the wafer is shifted parallelly in order to inspect a wafer surface of a next inspection region of the wafer.
According to the conventional method of inspecting a wafer surface, a height of the inspection region, which is detected during inspection of the inspection region, is fed back to compensate for a height of the next inspection region. Likewise, a height of the next inspection region is used for compensating for a height of a third chip, and so on. Therefore, when a height of the first inspection region is deviated far from an allowable limit, after a large number of chips are inspected, many chips of the wafer will be unreliable, thereby lowering productivity.